Page:Popular Science Monthly Volume 21.djvu/45

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But how different from the others, both in character and history, is the sense of touch! Having with them a common origin, like them it is resident in the outer skin, but it is active alike all over the body; the touch of the finger tips may be more delicate than that of the palms, but it is only a quantitative difference. The sense of touch is the fundamental sense. All the other senses have to render their data into its terms before they can be understood by the mind. Animals can live without sight, hearing, taste, or smell, but the presence of the sense of touch seems a necessary condition of animal existence. The other senses are means of self-preservation; the sense of touch is the manifestation of an animal's existence.

The senses, then, all originate from the outer covering; this covering has from the beginning a special sensation from the resistance to external pressure; this property it retains throughout the animal kingdom. The other sense-organs appear as specialized parts of this universal sense-organ; morphologically they are only parts of the skin, rendered more sensitive than the normal skin.

All the evidence seems to point one way, to the conclusion that the other senses are all modifications of the sense of touch. That such is probably the fact seems to be generally admitted. What I have tried to show is our ground for that conclusion, and that what was with Democritus a random speculation is with us fast assuming the nature of a scientific truth.


THAT a near object of small dimensions presents an aspect slightly different to each one of a pair of eyes directed upon it, has been known for more than two thousand years; but no application of this knowledge was ever made until some time after the beginning of the present century. The analysis of binocular vision is one of the products of modern investigation, and the stereoscope is its direct outcome. That vision with two eyes is greatly preferable to what the ancients accorded to Polyphemus is fully appreciated by every one who possesses a pair of healthy visual organs and a stereoscope, but who at any time has been so unfortunate as to suffer a temporary injury that reduces him for a few days to the condition of the classic monocular giant. Familiar as he may be with the truth that the perspective effect of a fine painting is better appreciated when one eye is closed,

  1. Expanded from an address before the Photographic Section of the American Institute, delivered March 7, 1882.